This invention relates to material hold-down mechanism for a stitching machine, particularly as employed with book-type templates as on an automatic digitized stitching machine for making footwear and the like.
This invention was initially developed for the manufacture of footwear such as shoes and boots, and for convenience will therefore be explained largely in that environment. However, it will be understood that the invention is applicable to other environments involving stitching together of layers.
In shoe manufacture, the stitching together of several overlapping layers is commonly accomplished with the aid of a multiple sheet template with the sheets in hinged relationship similar to a "book", the individual layers of material to be stitched, e.g. leather, cloth, etc., being selectively retained between the template sheets. Elongated configurated openings in the template sheets are aligned with each other to allow the stitching needle to penetrate the entire template for stitching the layers together.
In recent years, automatic digitized stitching machines have been available wherein the template book, with the layers of material therein, are clamped to a feed control on the bed of the stitching machine. The feed control incrementally shifts the templates in two horizontal dimensions on a programmed basis to achieve the predetermined stitching pattern during vertical reciprocation of the needle and needle bar. In such an arrangement, it is apparent that the thickness, i.e. height, of the template book on the bed of a machine will depend on the number of layers to be stitched as well as the individual thickness of the layers. Moreover, since the layers are typically of differing dimensions and shapes, the template and material thickness or height will vary from portion to portion thereof.
During the stitching operation, the top layer of material is engaged by the material hold-down device which projects into the opening of the uppermost leaf of the template. This device typically has a small cylindrical nose portion surrounding the reciprocating stitching needle, with its end surface engaging the material prior to the needle penetrating the material. A conventional hold-down for this purpose is depicted in the drawings, specifically at FIGS. 7 and 8. Such units comprise costly specially made castings.
This conventional hold-down has presented problems, particularly when used in the automatic digitized stitching machines. Specifically, the shoulder projecting laterally above the nose repeatedly strikes the edges of the openings of the top template sheet, causing damage and sometimes breakage of the hold-down unit, causing damage to the template, and causing excessive wear on the machinery because of the lateral stresses applied. In efforts to minimize this, the template openings through which the needle projects have been enlarged to effect more lateral space between the needle and the edges of the template. While this does lessen the instances of the hold-down striking the template, it also lessens the clamping effectiveness on the material near the needle, and even allows some narrow material edges to remain unclamped. This too often results in reject products. Furthermore, it has been determined that the strength of the conventional hold-down is lacking in response to certain lateral stresses applied thereto, because of its construction, so that when the power feed causes the template to strike the hold-down, the latter readily breaks. This causes costly downtime as well as reject product.